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SDS Timing Wierdness!!


Nigel

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Hey guys!

 

When I first got my 240Z Turbo with SDS EM3-6F (non-intercooled and running 7psi boost max) on the road last year, I ran into a problem with it losing power at full throttle up around 4500 rpm and beyond, most noticeably in 3rd gear and higher. I thought it might be fuel related, so I replaced the ancient 280ZXT injectors and fuel pump with cleaned 460cc RX-7 injectors and a Walbro 255lph pump over the winter.

 

Today was the first day I've had the car on the road this year, and I took the car to a drag strip for the first time. It was my first time on a drag strip too. Right off the bat, I had the same problem as I did last year. But the AF ratio guage showed nice and rich. So, I had a friend ride in the car with me and watch the timing readout. At full throttle, he was reading out timing numbers to me like 16 and 13!!!

 

Now, I have the ignition curve starting out at 18 deg advance at idle and ramping up to 37 deg at 2750 and staying there the rest of the way. My MAP retard values start pulling out timing at about 2psi of boost and ramp up to 14 deg at 5psi and stay there. So, at full boost, my total timing should be no lower than 23 deg, not down at 13!

 

I thought maybe the knock sensor was doing it, but if I rev the engine up to 6000 rpm in neutral, I have to have the sensitivity set to 10 before it starts pulling back timing. I had the sensitivity set as low as 5 and my retard value down at 3 degrees for the runs on the track but I was still seeing timing values as low as 13.

 

I'm at a loss as to what's going on. The car could be really fast if I could just get this sorted out. I did a best of 15.1 at 7 psi, and I'm sure I could get into the mid 14's if the timing wasn't all screwed up.

 

Any ideas?

 

Nigel

'73 240ZT

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Well, it looks like the computer may have legitimately been pulling out timing. I checked my plugs yesterday and discovered that 2 were bone white, and that's with plugs one step colder! So it looks like 2 injectors are flowing significantly less than the other 4, and there could have been pinging on those two cylinders, resulting in the timing being retarded. I had all the injectors cleaned, but the two in question were done by a different shop than the other 4. I did a flow test and it looks like they're spraying ok, but I don't have a means to accurately measure the volume. In the process of testing, I discovered that 1 of other 4 is leaking! So, needless to say, I'm pissed off! I thought I had fuel supply covered... damn.

 

Nigel

'73 240ZT

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Guest Zcarsmakemyheadhurt

First off did you shut the engine off at WOT in the top of third then look at the plugs? Thats the only way you are going to know if your going lean by reading plugs. Tune this thing on race fuel, I don't have igntion programablity on my ECM and I lock the igntion out at 32degrees no problem lots of power. I would loose the knock sensore feature for now it sounds like your ECM is trippin you should be able to run between 28-32 with ease depending on your injector size. What are you running for pump and injector? Let me know interesting problem, sounds like it could be solved in the hand set.

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Well, I checked my plugs after the 200 mile roud trip to the track and back, and like I said, two were bone white. They looked like they had just been taken out of the package. The other 4 plugs looked like what you would normally expect after a couple hundred miles of use , tan/grey deposits. To me that indicates two cylinders running lean. And keep in mind, these are colder plugs.

 

So I think it was pinging on those two cylinders at full throttle, and the ECU was pulling back timing. I was tempted to shut off the knock sense feature at the track, but I was affraid to do so in case it was doing so legitimately.

 

I went back to the place where I got 4 of the six injectors cleaned today to have them redo the one that was leaking, and match the two (again, these 2 were not done by them) that corresponded to the two white plugs to the leaking one. They should be able to confirm if there is a significant difference in flow rates.

 

As you may recall from my first post, these are 460 cc RX-7 injectors and I'm running a Walbro 255lph pump.

 

Nigel

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Guest Zcarsmakemyheadhurt

Sorry man, it didn't compute when you said the injector displacement the first time. No doubt about it good move on having the injectors flowed, I hate it when a engine is lost to injectors. If your not going crazy on the boost high timing should be easy if you have a good intercooler set up. Let us know how it turns out.

 

Alex C

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My MAP retard values start pulling out timing at about 2psi of boost and ramp up to 14 deg at 5psi and stay there. So, at full boost, my total timing should be no lower than 23 deg, not down at 13!

You said you ramp to 14* @ 5#. Hope you meant to say 14* @ 15# because taking out 14* @ 5# will kill performance. You are on the right track with the 2 plugs running lean.

 

Good luck.

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Hi guys...

 

Well, I should get the injectors back tomorrow (Thursday), and hopefully they'll have everything sorted out. I never would have guessed that I would have had so much trouble getting 6 injectors to work right, even after a rebuild. I sold my ancient 280ZXT injectors to a mechanic friend which he flow tested and they still work great with no leaks!

 

And no Scottie, that wasn't a typo. I really do have my timing that low. That's a remnant from my experimentations last year when I was trying to figure out why it wasn't running right. I know it can go much higher than that, I just didn't get around to changing it back. When I get the car out again, I'll redo the retard curve. Unfortunately, that won't be for another week and a half :(

 

Nigel

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Well, so much for that theory... I got the injectors back today. Aparently, the 2 injectors in question are flowing as well as the others. So, now I have no idea what's going on. I'm going to run those 2 injectors on different cylinders and see if the apparent leaning out follows them. I may try replacing the knock sensor too. Does anybody know a year and model of GM vehicle to give to the parts guy to get a replacement? Also, what knock sensitivity are you all running?

 

I've also considered crank angle sensor problems, but I never get an RPM ERR message (except when my fast idle shuts off, but that's another story :sour: ). You could lift the engine with my sensor mouting bracket and the gap is within specs. The wires and sensor are no where near the ignition or alternator. I never get any display wierdness.

 

I'm running out of ideas. And I'm getting very discouraged...

 

Nigel

'73 240ZT

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Hi Nigel - It sounds like what was happening with my SDS when I first installed it - the GM sensor would see the valvetrain noise as knock. I would recommend going back to the nissan knock sensor and upgrading your SDS software to Version 11. This version has much better knock filtering and O2 sensor feedback control.Also has a knock indicator display which lets you know when the computer is sensing knock. I'm a lot happier with this version. It cost me 45 CDN to upgrade. I went to 3 BAR map sensoring also :-D . Served me good last night at Grand Bend - Ran a 12.7 at half throttle with the wastegate open. Big boost creep. As they say - Back to the laboratory!

Cheers- Doug

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Hi Doug!

 

I was hoping to see you at the track last week. I heard something about a coolant leak? I was talking with a friend of yours there. I forget his name. He has a blue 240 Turbo. I believe he won the eliminations?

 

Well, for $45CDN, I'd be willing to give the software upgrade a shot. I guess it would it be reasonably safe to give the car a run with knock sensing turned off to test the hypothesis that the knock sensor is overreacting. With 94 Octane gas and only 7 psi, it does seem unlikely that it would detonate without some really screwed up programming. How long was the turn around time for the upgrade?

 

Nigel

'73 240ZT

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Yes - coolant leak got me - and no time to tune the new setup. A new chip is just an email to Ross away. I gave him my setup specs and he had the new chip in the mail the next day. The chips are one-time burnable so you just chuck your old one in the trash. Make sure to use the chip puller they send. They may charge a bit more if you don't have the puller. Talk to you later

Doug

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I suspected it may just be a chip swap. But I wasn't sure if they'd trust the customer to do it themself. No biggie for me though. We have the pullers at work. I'll talk with Ross tomorrow. I should get the chip before the end of the week. With any luck that will cure my fast idle shut off RPM ERR problem too.

 

Nigel

'73 240ZT

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To cure that on my car I used a reversed biased diode to ground on the terminal of the fast idle sol. It's the collapsing magnetic field in the solonoid that gives the computer a zorch. If you put a diode from the terminal to ground, it forms a short circuit when you shut off the fast idle - presto - no voltage spike to the computer. I have one on my linelock also. The polarity of the spike from a collapsing magnetic field is opposite in polarity to the input voltage - so the diode conducts nothing until the fast idle is shut off. Ross will send you a diode and a diagram if you let him know you are having trouble with this. Cheers - Doug

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I was thinking over the fast idle situation this morning, and the same thing occured to me. I do have the power wire for the fast idle solenoid bundled with the crank angle sensor cable. The solenoid is switched through a relay, so it's not affecting the ECU directly, but the noise pickup in the CAS cable appears to be enough. Are you talking about a Zener diode to correct this? I can get my hands on say, a 16 V Zener easily enough.

 

I e-mailed Ross today, and he got back to me already. Apparently the price has gone up... it'll be around $100 for the chip, tool, shipping and tax. Or, I can send it to them and they'll install it for $75 plus $15 shipping (not to mention my shipping cost there), and they will install some filter caps on the CAS inputs to the microprocessor. I think I may ask if they can just mail me the caps and directions where to put them. I've populated surface mount circuit boards by hand, so I'm sure I could handle the installation.

 

Nigel

'73 240ZT

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Did you mention that you're a member of Zcar.com? That nets you a 10% reduction across the board. I guess that I get a bit of a break with SDS - I've dealt with them for a while now. This is my third software upgrade :? I just used a normal old 4001 diode on my fast idle - from the terminall to the ground at the sol. Very simple and quick to do. Let me know how it works for you - Doug

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Just a regular diode then? I don't think you ment to say "reversed biased" in that case, which would be a Zener. I've got lots of regular diodes kicking around. So, it would have to be the white stripe (I always get cathode and anode mixed up) to the solenoid terminal. Makes sense...

 

I emailed Ross about the discount...

 

Thanks for all the help Doug. I hope this finally gets the car running the way I know it can. Are you going to Cayuga? Hopefully we can actually meet in person one of these days.

 

Nigel

'73 240ZT

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Yup - just a regular diode. Put in in and then test it with an ohm meter. If you have continuity between the terminal and the ground - It's in the wrong way. I don't think I can make it to the track in July - Likely will be back at work - somewhere. Don't think I'm going back to Iraq any time soon. Maybe South America this time out. I do try to make it to the strip at Grand Bend for Test-n-tune on Wed or Fri nights. Email me if you are interested in going out for that. The way my car is making power right now would make it very unpredictable on the road course. :shock::shock: Could find myself going off a corner bassackwards.

Cheers - Doug

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Guest Zcarsmakemyheadhurt

Disable the knock sensore at least untill you start spraying that car 150 on the NOS, or running a earth shaking amount of boost. Those are the times you need those types of precausions. I personaly wouldn't ramp the ignition retard in most 7:4.1 engines till 15psi. Disable the knock sensore bring the timing to 32 at 10psi then check the plugs after WOT shut down. Or buy a EGT.

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